The invention concerns an elastic seating element for a fluid flow cutoff device. Elastic seating elements are utilized in connection with cutoff devices of the type including a sealing part whose apertured surface slides across the seat during opening and closing movements. A seating element for use in such an environment is disclosed for example in U.S. Pat. No. 2,973,181. The supporting part of the seating element of that patent is designed in the form of a short cylindrical tube section, placed in telescopic fashion onto a section of a flow-through fitting which is tapered and protrudes into the housing of the shutoff device. The seating part of this known elastic seating element is designed in the form of a outer flange at its end facing the sealing part. The seating part has a circular surface against which the sealing part is pressed, thus forming a surface seal, and the sealing part will move across this surface when the shutoff device is actuated. If the sealing part is formed by a flat disk (e.g., the shutoff device comprises a rotary slide valve) the seating surface of the seating part will also be flat. If the sealing part is a cylindrical rotary piston (for example, if the shutoff device consists of a cock), the seating surface will then be surface complimentary, in other words designed in the shape of a cylinder.
This known seating element has the disadvantage that it is subject to failure if the fluid to be cutoff contains solid particles. When the sealing part moves relative to the seating element, the solid particles will enter the contact area between the seating part and the sealing part which acts as the sealing surface. They will have an abrasive effect there which will very quickly lead to a leakage of the shutoff device. This known seating element will therefore have an undesirable short service life, especially if the shutoff device is used frequently. This deficiency is especially critical if the shutoff device, for example, a rotary slide valve or a rotary piston cock, it utilized for cutting off the heating means of motor vehicle heaters. This heating means, usually water, always contains molding sand residues and rubbed-off particles. Furthermore, the shutoff devices for heating systems of motor vehicles are turned on and off very frequently.
German Gebrauchsmuster (GM) No. 7,321,690 proposed an improvement in the service life of the elastic seating element for the sealing part of a shutoff device used for fluids carrying solid particles by designing the seating element in the form of a looping ring which is held in place by a collar which surrounds the flow through opening in the housing. In comparison with the above-discussed flat surface seal, this looping ring has all the advantages offered by a circular seal over a flat surface seal. The looping ring, serving as seating element, has also a certain skimming effect on the sliding surface of the sealing part so that fewer solid particles will reach the sliding surfaces and the grooving will thus be reduced although it cannot be eliminated completely. However, there arises another disadvantage during the movement of the sealing part, pressed against the looping ring, with the movement being parallel to the plane of the ring, which cancels in practice the advantages of this specific seating element which are attainable in theory, namely, the so-called rolling of the seal. Whenever the edges of the opening or openings, provided in the sealing part, are passing over the ring, dragging effects will occur which lead to an irregular rolling twist of the ring and as a result thereof to leakages. Furthermore, due to this rolling the solid particles carried by the fluid to be cut off will again be rolled or pressed respectively between the seating element and the sealing part so that grooves will form again and reduce the service life of the components.
An elastic seating element, described by the published German patent application No. 2,651,290, makes the attempt to combine the advantages of the above-described designs of seating elements while eliminating their disadvantages. This known seating element is primarily designed in the form of a cylindrical ring. The supporting part is designed as a ring of axial pins which can be pressed into corresponding recesses in the housing wall of the shutoff device. The front wall surface in contact with the housing wall and supporting the seating element is radially wider, approximately twice as wide, than the axially opposed front wall surface which slides at the sealing part. This seating element has an axial profile where the flow-through opening is strictly cylindrical throughout, and where the radial tapering from the greater outer diameter of the housing wall part to the smaller outer diameter of the seating element facing the sealing part occurs mainly at the side of the seating element facing the housing wall. Thus, the section of the seating element, which represents approximately one-half of the axial height and which faces the sealing part, is designed strictly cylindrically outside as well as inside, with right angles to the circular front wall surface. The section of this known elastic seating element which faces the sealing part has therefore the form of a short tubular section which rests at the sealing part with its front side which serves as a sealing surface. The radial width of this frontal area seal has a critical minimum size because a rolling of the seal will occur otherwise. Furthermore, the axial height of this cylindrical section of the seating element must not be made too great since the seal would then again have the tendency to roll. The right-angled arrangement of the transition between the cylinder wall surfaces and the front wall surface is used for the purpose of attaining a skimming effect at the sealing part. However, the actual result is still a surface seal of the type described above, with basically the same susceptibility to wear and tear as displayed by the flat surface seal discussed previously. The relatively smaller size of the sealing surface will cause a slight delay in the occurrence of a leakage of the seal. But the lengthening of the service life is definitely not proportional to the reduction in area because the reduction of the sealing surface will also lead more quickly to leakages. Furthermore, the surface friction between the seating element and the sealing part during the setting of the shutoff device is, in spite of the relative reduction in the sealing surface, still quite heavy, as is typical for any flat surface seal so that even this seating element requires rather great efforts for the setting of the shutoff device.
In view of this present state of art, it is an object of the invention to establish an elastic seating element for a shutoff device with a sealing part which slides along the seat at the time of opening and closing, wherein the seating element exhibits a long service life even in case of the presence of a greater amount of particulate matter in the fluid to be cut off and insures a definite and complete seal of the shutoff device at high surface pressures, and requires minimum opening and closing forces.